docs: def signalStrength(self):
          """ Checks the modem's cellular network signal strength
          
          :raise CommandError: if an error occurs
          
          :return: The network signal strength as an integer between 0 and 99, or -1 if it is unknown
          :rtype: int
          """
          csq = self.CSQ_REGEX.match(self.write('AT+CSQ')[0])
          if csq:
              ss = int(csq.group(1))
              return ss if ss != 99 else -1
          else:
              raise CommandError()